1. Field of the Invention
The present invention relates to shoe sole and heel constructions and, in particular, to such constructions with fluid-filled cavities for providing cushioning.
2. Description of the Prior Art
Various types of shoe sole and heel constructions having fluid-containing cavities have heretofore been provided, such constructions being disclosed, for example, in U.S. Pat. Nos. 4,237,625, 4,358,902, 4,577,417, 5,375,346 and 5,416,986.
These patents disclose a molded outer sole and heel structure which has downwardly projecting heel and metatarsal bulges molded therein to define cavities and a passageway extending between the cavities. Air or other fluid, at atmospheric (or other) pressure, moves back and forth between the cavities through the passageway during movement of a person wearing the shoe.
These prior sole and heel structures have provided cushioning for the user's foot and have also provided forward thrust which facilitates walking or running movements. These bulges usually, however, prevent the member from having an exterior flat portion in the heel and sole portion of the outsole which limits the versatility of the shoe. Additionally, these bulges tend to produce a lateral instability in the shoe, causing the shoe to tilt laterally inwardly or outwardly in use, resulting in pronation or supination of the wearer's feet.
Additionally, the passageways connecting the bulges are usually large and must be properly sized to prevent large quantities of air from residing therein, where it provides no cushioning.